Canadian wildfire smoke returns to Wisconsin

Much of the Upper Midwest was dealing with swaths of unhealthy air this past weekend because of drifting smoke from Canadian wildfires. It's covering the northern region of the United States at a time when people want to be enjoying lakes, trails and the great outdoors.

Wisconsin, most of Minnesota, and parts of Montana and North Dakota were ranked “unhealthy” for air quality on a U.S. Environmental Protection Agency map. Part of North Dakota that is home to Theodore Roosevelt National Park and other tourist attractions was ranked “very unhealthy,” some of the worst air quality in the nation.

The air-quality index measures how clean or polluted the air we breathe is on a daily basis. The index focuses on the health effects that might be experienced within a few hours or days after breathing polluted air.

The index is calculated based on ground-level ozone, particle pollution or particulate matter, carbon monoxide, sulfur dioxide, and nitrogen dioxide. Ground-level ozone and airborne particles are the two pollutants that pose the greatest threat to human health in this country.

The index ranges from green, where the air quality is satisfactory and air pollution poses little or no risk, to maroon, which is considered hazardous. That level comes with health warnings of emergency conditions where everyone is more likely to be affected, according to the Environmental Protection Agency's AirNow page.

In Minnesota, “If you have a nice pork loin you can hang from a tree, it'll turn into ham,” quipped Al Chirpich, owner of the Hideaway Resort near Detroit Lakes, where people come to enjoy tree-lined Island Lake for fishing and other water activities.